The entire disclosure of Japanese Patent Application No. 10-74800 filed on Feb. 16, 1998 and International Application No. PCT/JP99/00655 filed on Feb. 15, 1999, including specification, claims and summary is incorporated by reference in its entirety.
1. FIELD OF THE INVENTION
The present invention relates to frozen food and a process for preparing the same. More particularly, the present invention relates to frozen foods and a process for the preparation of frozen foods, including particularly fresh and raw fish flesh and shell and meat, which can remarkably improve taste and flavor of such foods, even after such foods or food materials or processed foods or food materials prepared by processing such foods or food materials was defrosted.
2. DESCRIPTION OF THE RELATED ART
In order to store foods or food materials for a long period of time, various difficulties have to be solved. Foods or food materials can be stored at ambient temperature for a very limited and short period of time and it is generally impossible to store foods or food materials for a long period of time even at low temperature. There is the limit in storing foods or food materials for long even at temperature lower than 0xc2x0 C.
In order to allow storage of foods or food materials for a certain period of time particularly at ambient temperature and in some cases at low temperature, it is also required to prevent the decaying of foods or food materials.
The decay of foods or food materials is caused by the growth of organisms, such as putrefactive or decaying bacteria, fungi, etc., in foods or food materials. The growth of such organisms in foods or food materials may greatly depend upon the water activity in foods or food materials as well as upon conditions such as temperature, etc. in surroundings of storage of foods or food materials. The growth of organisms including putrefactive bacteria, etc. is accelerated at ambient temperature or at temperature higher than ambient temperature, so that the speed at which foods or food materials decay becomes faster as temperature becomes higher, and foods or food materials may accordingly become likely to decay at a faster speed and for a shorter period of time. On the other hand, while foods or food materials are stored at low temperature at which organisms are unlikely to grow, the multiplication of organisms can be controlled and the decay of foods and food materials can be prevented. However, the storage of foods or food materials at such low temperature may cause new problems upon thawing frozen or refrigerated foods or food materials, as will be described hereinafter.
Moreover, unless foods or food materials keep the water activity at a predetermined level, organisms including putrefactive bacteria etc. cannot grow in foods or food materials so that the decay of foods or food materials may little be caused in such a dry state. Therefore, the water activity in foods or food materials has to be controlled at a level lower than a predetermined one in order to prevent the decay of foods or food materials by putrefactive bacteria and so on.
Currently, the most common and useful way of controlling the water activity in foods or food materials at a low level may include a process of adding an additive such as a salt and/or a saccharide. As a matter of course, however, the addition of such an additive provides the foods or food materials with the taste or flavor originated from the additive. The taste originated from the additive can little be perceived, that is, that the taste or flavor of the foods or food materials cannot be spoiled by the addition of the additive thereto, if the additive would be used in a very small amount. The addition of such a very small amount of a salt and/or a saccharide, however, cannot achieve the object of controlling the water activity in foods or food materials at a low level. And this may result in a decrease of the effect of preventing the decaying of foods or food materials. This also indicates that, as such a salt and/or a saccharide have or has to be added in a certain amount in order to prevent the decay of foods or food materials, the taste originated therefrom is also provided to the foods or food materials and as a consequence the own taste and flavor thereof might be spoiled to some extent. In this sense, such an additive including a salt, saccharide or the like cannot be added to fresh or raw food materials in order to control the water activity in the foods or food materials, as long as it is eaten in a fresh or raw state, so that the process for adding the additive to such fresh or raw foods or food materials cannot be adopted for this purpose.
Currently, only the way of storing fresh or raw foods or food materials for a certain period of time without causing decaying the foods or food materials and adding any salt, saccharide, or the like thereto is to freeze or refrigerate fresh or raw foods or food materials or keep them in cold storage. The biggest defect relating to the way of freezing or refrigerating fresh or raw foods, etc., however, resides in that the frozen or refrigerated foods etc. become dry or cause drying to whiteness or whitening or cell-decomposing particularly on the surfaces of the frozen foods or food materials during freezing or cold storage as well as that the thawing or unfreezing of the frozen foods or food materials may often spoil the taste or flavor of the thawed or unfrozen foods or food materials. In order to lessen the defect of the storage process for freezing or refrigerating such fresh or raw foods or food materials as much as possible, it is required to strictly manage conditions including temperature for freezing or refrigerating or keeping in cold storage such fresh or raw foods or food materials. The strict management of the frozen or cold storage, however, requires a large amount of expenses and labor. Moreover, even if frozen or refrigerated foods or food materials would be stored under such strictly managed conditions by using such a large amount of expenses and labor and it would be thawed carefully under strictly managed conditions, the problem may remain still unsolved that the original taste or flavor etc. of foods or food materials may be spoiled unavoidably by thawing or unfreezing the frozen or refrigerated foods or food materials.
The problem with the spoilage of the taste, flavor or the like of the thawed or unfrozen foods or food materials, however, is the issue relating to the mechanism of freezing or refrigerating foods or food materials, and the issue cannot be completely solved simply by adding an additive including preservative or the like.
In order to solve or improve the problem with the drying to whiteness or the whitening of frozen or refrigerated foods or food materials during storage by the freezing or refrigerating process, there have been used, for examples, ways of adding a variety of additives to foods or food materials or spraying a solution containing such additives thereonto or dipping them in such a solution. The storage of foods or food materials by means of the freezing or refrigerating process by using such additives, however, is not always effective and satisfactory.
Further, various attempts have been made to improve storage performance of foods or food materials by coating the foods or food materials with a proteinaceous gel including gelatin, collagen, etc. or the like and then freezing or refrigerating the coated foods or food materials. These processes can improve the storage performance of foods or food materials to some extent.
When the foods or food materials processed by freezing or refrigerating them in the above manner are thawed or unfrozen, however, the problem with the spoilage of the taste or flavor of the foods or food materials cannot be solved completely or satisfactorily.
Moreover, it is reported that, in order to improve the storage performance of foods or food materials by coating them with gelatin or the like in the above manner, a solution containing gelatin has to be used in an amount as high as at least 1% by weight. The coating with such a high concentration of gelatin or the like naturally leads to spoiling the taste and flavor of the foods or food materials upon thawing or unfreezing the frozen or refrigerated foods or food materials.
Various attempts have so far been made to solve the problems present in the conventional processes for freezing or refrigerating foods or food materials.
One of the attempts is to use polylysine as a food preservative, which is one of naturally occurring amino acid polymers and which is known as a food additive having a wide antimicrobial spectrum against a variety of organisms.
It is extremely useful to use polylysine having a wide-range antimicrobial spectrum as a food preservative agent in order to prevent the decay of foods or food materials during storage for a long period of time. Polylysine itself, however, does not function preventing the spoilage of the taste or flavor of foods or food materials upon unfreezing or thawing the frozen or refrigerated foods or food materials. Moreover, polylysine is expensive so that it is less economic to use polylysine solely for these purposes. It is therefore suggested that polylysine is used together with a different antimicrobial agent as a combination agent.
A polylysine-gelatin mixture formulation for use in storing foods or food materials is proposed as such a combination agent, which is composed of polylysine and gelatin as major components (Japanese Patent Publication (laid-open) No. 9-98,754).
It is disclosed therein that the polylysine-gelatin mixture formulation can prolong the period of time during which a natural taste or flavor of foods or food materials is kept as it is and without being spoiled, compared to the case where polylysine or gelatin or a material decomposed therefrom is used solely.
The polylysine-gelatin mixture formulation, however, cannot satisfactorily prevent the spoilage of the taste or flavor of foods or food materials processed therewith, when used solely, due to the breakdown of cells of the foods or food materials by unfreezing or thawing the frozen or refrigerated foods or food materials.
Therefore, the present invention has the object to provide frozen foods or food materials that can keep their original taste and flavor without being greatly spoiled by unfreezing or thawing the frozen foods or food materials after cold storage for a long period of time. The present invention has another object to provide a process for preparing such frozen foods or food materials.
In order to achieve the objects as described above, the present invention provides frozen foods or food materials comprising foods or food materials and an alkali metal halide or an alkali earth metal halide, an alkali metal bicarbonate or an alkali earth metal bicarbonate, an organic acid and gelatin.
Further, the present invention provides frozen foods or food materials further comprising polylysine in addition to the components as described above.
Organisms may grow while unfrozen or thawed foods or food materials are placed or stored in such a non-freezing state for a certain period of time after the frozen foods or food materials were unfrozen or thawed. The polylysine can prevent the growth of organisms including decaying bacteria and so on in foods or food materials.
Moreover, the present invention provides a process for preparing frozen foods or food materials containing an alkali metal halide or an alkali earth metal halide, an alkali metal bicarbonate or an alkali earth metal bicarbonate, an organic acid and gelatin, the process comprising the food-processing step of processing a food or a food material to be frozen or refrigerated with an alkali metal halide or an alkali earth metal halide, an alkali metal bicarbonate or an alkali earth metal bicarbonate, an organic acid and gelatin; and a food-freezing step of freezing or refrigerating the processed food or food materials in cold storage.
The frozen foods according to the present invention can present the great advantages that they can be stored in a cold state for a prolonged period of time as well as that the original taste or flavor of the foods or food materials is little spoiled upon unfreezing or thawing the frozen or refrigerated foods or food materials. The freezing process according to the present invention can prevent a decrease in the taste or flavor of the thawed or unfrozen foods or food materials due to drying to whiteness or whitening of foods or food materials during cold storage, the breakdown of cells by thawing or unfreezing or for other reasons, even if the foods or food materials are unfrozen or thawed after cold storage for a long period of time.
Other objects, features and advantages of the present invention will be apparent in the course of the specification and appended claims.
The frozen or refrigerated foods or food materials according to the present invention can be prepared by processing foods or food materials to be frozen or refrigerated with an alkali metal halide or an alkali earth metal halide, an alkali metal bicarbonate or an alkali earth metal bicarbonate, an organic acid, and gelatin and polylysine, if needed or advisable.
Foods or food materials for use with the present invention are not limited to particular ones and any food or food material may be used as long as it is frozen and thawed before use. Foods or food materials may include, for example, fresh or raw foods or food materials including vegetables, fish, shell, animal meats, and so on, processed foods or food materials including edible grains, cereals, grain or cereal products including noodles, dishes, and so on. Foods or food materials applicable to the present invention are not limited to particular types of foods or food materials, and the present invention can be applied to any type of foods or food materials as long as they can be frozen and then thawed for use or application.
The alkali metal halide or the alkali earth metal halide for use as a component of the frozen foods according to the present invention may include, for example, a halide of sodium, potassium, magnesium, etc., such as sodium chloride, potassium chloride, magnesium chloride, and so on. The alkali metal halide or the alkali earth metal halide may be used singly or in combination with two or more. The preferred example of the alkali metal halide or the alkali earth metal halide is sodium chloride.
The alkali metal halide or the alkali earth metal halide may be used in an amount ranging typically from approximately 0.1% by weight to 5% by weight, preferably from approximately 0.2% by weight to 3% by weight, and more preferably from approximately 0.3% by weight to 2% by weight, with respect to the total weight of the food or food material, although the amount of the alkali metal halide or the alkali earth metal halide may vary with the kind or type of the raw material or with other conditions.
The alkali metal bicarbonate or the alkali earth metal bicarbonate for use as a component of the frozen foods according to the present invention may include, for example, sodium bicarbonate, potassium bicarbonate, and so on. The alkali metal bicarbonate or the alkali earth metal bicarbonate may be used singly or in combination with two or more. The preferred example of the alkali metal bicarbonate or the alkali earth metal bicarbonate is sodium bicarbonate.
The alkali metal bicarbonate or the alkali earth metal bicarbonate may vary with the kind or type of the foods or food materials to which it is applied or with other conditions, and the alkali metal bicarbonate or the alkali earth metal bicarbonate may be used in an amount ranging typically from approximately 0.01% by weight to 0.5% by weight, preferably from approximately 0.05% by weight to 0.3% by weight, and more preferably from approximately 0.1% by weight to 0.2% by weight, with respect to the total weight of the food or food material.
In addition to the components as described above, the frozen foods or food materials according to the present invention contain the organic acid. The organic acid for use in the present invention may include, for example, acetic acid, lactic acid, adipic acid, malic acid, citric acid, fumaric acid, oxalic acid or the like. The organic acid may be used singly or in combination with two or more. The preferred examples of the organic acids are acetic acid, citric acid, lactic acid, and a mixture of two or more.
The amount of the organic acid to be contained in the frozen foods of this invention may range typically from approximately 0.0005% by weight to 0.05% by weight and preferably from approximately 0.001% by weight to 0.01% by weight based on the weight of the food or food material The amount of the organic acid may be varied in accordance with the type of the food or food material.
The other component for use with the frozen foods according to the present invention is gelatin. Any kind of gelatin can be used as long as it can be typically used as a food additive. As such gelatin, a purified gelatin that is purified to a taste-free or tasteless state is particularly useful.
The amount of gelatin may vary with the kind or type of the food or food material, the kind or type of gelatin, etc. or with other conditions, and gelatin may be used in an amount ranging typically from approximately 0.05% by weight to 10% by weight and preferably from approximately 0.1% by weight to 5% by weight, with respect to the weight of the food or food material.
The frozen foods according to the present invention may contain polylysine as needed or advisable. The greatest advantage produced by the use of polylysine resides in the fact that the multiplication of organisms including decaying bacteria or the like can be greatly controlled, compared to the case where no polylysine is applied. In the case where no polylysine is used, decaying bacteria and other organisms may naturally grow faster in a shorter period of time in unfrozen or thawed foods or food materials after they are unfrozen or thawed and then placed or stored for a certain period of time.
Polylysine to be used optionally for the present invention is not limited to a particular type of polylysine as long as it can be added to foods or food materials. Particularly preferred is xcex5-polylysine that is a naturally originated food additive.
The amount of polylysine to be added to the frozen foods according to the present invention may typically vary with the kind or type of foods or food materials to be processed, the kind or type of gelatin or with other conditions, and it may range typically from approximately 0.05% by weight to 10% by weight and preferably from approximately 0.1% by weight to 5% by weight, with respect to the weight of the food or food material.
The frozen foods according to the present invention may be prepared by processing a food or food material to be frozen with a necessary amount of the components in the following manner.
As a food or food material to be frozen and stored in a frozen state in accordance with the process of the present invention, there may be used a food or food material in a fresh or raw state or in a non-cooked state, that is, in such a state that it is not prepared or cooked, or in a processed or cooked state, that is, in such a state that it is cooked or prepared e.g. by heating. More specifically, for instance, a food or food material, including animal meat, e.g., beef, pork, chicken, etc., fish, e.g., tuna, sea bream, squid, octopus, shrimps, etc., shell, vegetables, and so on may be processed by the process according to the present invention without pre-processing, including cooking, e.g., processing by heating, etc., or simply by cutting it into appropriate sizes or shapes.
The food or food material pre-processed as needed may be processed with the alkali metal halide or alkali earth metal halide, the alkali metal bicarbonate or alkali earth metal bicarbonate, the organic acid, and gelatin and, if needed, polylysine, in the manner as will be described hereinafter.
The frozen foods or food materials of the present invention may be prepared in accordance with any conventional method that can be applied to the process for preparing the frozen foods or food materials. The frozen foods or food materials may be prepared, for instance, by pre-processing a food or food material, as needed, then processing it with each of the components one after another, and freezing or refrigerating it. Alternatively, the frozen foods or food materials may be prepared, for instance, by pre-processing a food or food material, as needed, then processing it with a mixture of two components or more, and freezing or refrigerating it.
As the process for processing the food or food material with the components into the frozen food or food material according to the present invention, there may be used any conventional process for preparing frozen foods as long as it can use food additives and it can be applied to the preparation of the frozen foods or food materials according to the present invention. The process for the preparation of the frozen foods or food materials according to the present invention may comprise, for example, spraying a food or food material as a raw material, pre-processed as necessary or advisable, with a solution containing the components for use in preparing the frozen foods or food materials, or immersing or dipping the raw material in such a solution, removing the liquid therefrom, placing the processed raw material in a bag or container or wrapping it, and then freezing or refrigerating it in cold storage such as a freezer or refrigerator.